Setting of anchors in rocks ranging from friable or cohesion-poor rocks to non-cohesion rocks for stabilizing of walls requires special steps for obtaining a stable position of the anchor. During the formation of a bore hole in such rocks, the problems arise in that the walls must be stabilized for preventing their collapse after withdrawal of a drilling rod. It is known to drill in these cases with casings and to compress the bore holes with cement mortar with simultaneous withdrawal of the tube. In this method the injected cement mortar also penetrates into the immediate surrounding area of the bore hole. The hardened bore hole filling is then again drilled and an anchor is inserted in the thusly produced opening and fixed with cement mortar. With this procedure it is possible to set the anchors in the above mentioned types of rock; however, this can be done with a relatively high time consumption and costs.
Rock anchors are also known which are simultaneously used as drilling rods and therefore include a tubular base body provided with a drilling crown at its front end. The above mentioned base body is profiled for producing a binding action with a mortar casing and has a plurality of openings in its peripheral region. During the drilling the rinsing medium, for example water, is supplied through the drilling crown and the above mentioned openings. Then after the end of the drilling, a mortar suspension is supplied into the produced bore hole. Under the above mentioned conditions, the sufficient penetration of the cement mortar in the rock surrounding the bore hole is not achieved in many cases, and thereby an insufficient adhesion of the anchor is produced.
A similar problem arises in many cases during production of pile foundations composed of individual piles provided with anchors. When for example an alternating sequence of cohesion-poor or non-cohesion layers on the one hand, and relatively solid layers on the other hand occurs along a path corresponding to the length of the pile, special steps must be taken to insure that the pile over its entire length has an average cross-section sufficient for the static carrying capacity of the respective pile foundation. In this case it is impossible to produce an opening which subsequently is filled with concrete, since the cross-section of the opening in the region of the soil layer is always provided with narrowings and the availability of the average cross-section over the whole length of the pile cannot be guaranteed in addition to the above mentioned narrowings.
In the latter mentioned case there is of course the possibility of an encased drilling, to insure the required uniform cross-section, especially maintaining an average cross-section.
The above mentioned known processes are either very labor and cost intensive and require therefore an expensive machinery, or can be used only to a limited extent with respect to the coherence of the respective rocks.